Restore clear compaction status message

[cbusillo]

Objective

Restore the user-visible compaction status/update that makes context compaction feel intentional and recoverable. The goal is to give the user a concise signal when previous context has been compacted, without adding meaningful token overhead or noisy repeated messages.

This is separate from the image-history rate-limit work and the remote-compaction retry investigation. It tracks the product/UI feedback regression only.

Finish Line

Compaction displays a concise user-visible status message without adding model-visible token overhead.

Current Status

State: Active
Next action: Identify when the compaction message disappeared by comparing the v0.6.98 baseline with later local overlay changes, then restore the intended TUI status path in a focused PR.
Blocked by: None
Last verified: 2026-05-13 on stabilize/v0.6.98-known-good

Scope

• In: User-visible TUI/status messaging for context compaction events; tests or harness coverage proving the message appears when expected.
• Out: Changing compaction algorithms, remote-compaction retry policy, image-history compaction, or token accounting behavior.

Acceptance Criteria

• Compaction emits a clear, concise user-visible status/update in the TUI when appropriate.
• The message does not get inserted as expensive model-visible conversational content.
• Routine repeated compactions do not spam the transcript.
• A focused test or harness scenario covers the restored behavior.
• The stabilization parent issue is updated with the final verdict.

Relationships

Part of #63. Related to #68 because both affect perceived and actual context management, but this issue does not implement the image-history rate-limit fix.

Validation

Pending. Expected validation will include the focused test/harness scenario plus the repository-required ./build-fast.sh before merge.

Decisions

• Track this separately from the image-history fix so product feedback does not get mixed into token/rate-limit mechanics.
• Prefer a concise status/update over adding explanatory transcript prose that could increase model-visible context.

Open Questions

• What exact previous message text and placement felt best in dogfood?
• Should the status appear only for automatic compaction, manual compaction, or both?